1. Field of Industrial Use
The present invention relates to a fusing device for an image forming apparatus, such as an electrophotographic copying machine or printer.
2. Description of Related Art
Conventionally, a fusing device that fuses a toner image that was transferred to a recording material such as a transfer paper (recording paper) onto the recording material has been incorporated in an electrophotographic image forming apparatus. For this fusing device, a device is normally utilized in which toner is heated, pressurized and then fused onto the recording material.
Various fusing devices of this type have been proposed and utilized up to now and one of these currently being utilized is called a fusing belt type heat fusing device. In Japanese Unexamined Laid-open patent HEI 6-318001, one example of a fusing belt type heat fusing device has been proposed. As shown in FIG. 6, this fusing device is comprised by a fusing roller 91, a heating roller 92, a fusing belt 93, and a pressure roller 94. The fusing roller 91 maintains a fixed gap with the heating roller 92 and is disposed parallel to the heating roller 92. The fusing belt 93 is an endless type belt and is wrapped around the fusing roller 91 and the heating roller 92. The pressure roller 94 makes contact with the fusing roller 91 through the fusing belt 93.
In the fusing device of FIG. 6, the fusing roller 91 is rotated in the direction of arrow a in the figure by means of a drive means (not shown in the figure). The fusing belt 93 also moves in the same direction following the rotation of the fusing roller 91 which drives the heating roller 92 and the pressure roller 94 to rotate. Further, along with the rotation of the fusing roller 91, each portion of the fusing belt 93 is heated by means of the heating roller 92 prior to arriving at a nip portion 95 between this belt and the pressure roller 94. Recording material S1 on which is transferred a toner image T1 is passed through the nip portion 95. The toner image T1 is fused to the recording material S1 by the heat of the fusing belt 93 and the pressure between the belt and the pressure roller in the nip portion 95. Moreover, guide rings 96 are provided on both ends of the heating roller 92. The fusing belt 93 is guided by these guide rings 96 preventing the belt from moving diagonally.
Furthermore, in this fusing device a tension roller 97 makes contact with the upstream side of the heating roller in the fusing belt movement direction against the outer surface of the fusing belt 93. The tension roller 97 functions both to supply offset suppression oil and to clean the belt. The belt surface on the side (downstream of the fusing belt 93 in the figure) that is preheated by means of driving the fusing belt 93 by the fusing roller 91 is deemed the stretched side 931 which transmits tension to the heated surface of the belt.
For the fusing device of Japanese Unexamined Laid-open patent HEI 6-318001, the tension roller 97 makes contact with the loose side 932 of the belt 93 which is a nonheated surface. The inventors found that on the loose side 932 of the belt 93, there was traveling unevenness of the belt (belt jumping) such as rising and falling waves on the ideal belt advancing surface of the fusing belt 93. It was confirmed that this traveling unevenness of the belt caused a sinking portion 933 that sinks toward the heating roller 92 of the fusing belt 93, and further resulting in the end surface 934 of the fusing belt 93 very unnaturally rubbing against the guide rings 96, and belt twisting occurring more easily. Thereby, problems such as the occurrence of edge cracks 935 on the belt 93, and rippling 936 caused damage to the belt. It was confirmed that when the distance between the tension roller 97 and the heating roller 92 was increased, this problem was more obvious.
It was further confirmed that because the fusing belt 93 jumps, a stable application of separation agent from the tension roller 97 to the fusing belt 93 could not be performed.
The above-mentioned problem of damage to the belt is not a problem restricted to the belt feed mechanism in a fusing device. It also occurs in the belt feed mechanism utilized in a document feed device and a belt feed mechanism utilized in a belt photoreceptor.